Jennifer Aniston is seeking treatment at The Chung Hua Institute in Santa Monica for a knee injury she suffered during her romantic getaway to Kauai with beau Justin Theroux.

We're told the Friends star spent over two hours seeing a specialist.

A source tells X17online exclusively:

"Jen has been in extreme pain for the past two weeks. Surfing isn't really her thing, but she gave it a try with Justin. She didn't think her injury was that bad, but since they got back from Hawaii, her knee has gotten worse."